PostScript (i.e. PS) is a programming language for describing page contents in the computer image processing technology, which is developed by Adobe Company and widely used as page description in most of software for processing texts, graphics and images. PS has become an industry standard in the field.
Portable Document Format (i.e. PDF) is an electronic document format for describing page contents, which was developed by Adobe Company. Generally, for the same page content, a PDF file has a smaller size and a more compact structure than those of a PS file.
Raster Image Processor (i.e. RIP) is a processor for transforming page description in PS or PDF to raster images and outputting in raster imaging devices (e.g. phototypesetter, computer-to-plate equipment and printer). A RIP system mainly comprises an RIP user interface for providing users with a user-friendly graphical interface, an RIP kernel for transforming page description in PS or in PDF to raster bitmaps, and a driver for outputting the raster bitmaps to raster devices.
The term “mark” in the present disclosure generally refers to various marks to be added to margins of a page to be output, like collimating marks, clipping marks, step wedges, color plate names, margents, job file names, outputting times, page numbers, customized marks defined by a user, and so on.
The term “job file” in the present disclosure refers to a description file of pages as filed to a RIP device for rasterizing and printing. A job file is generally a PS file, a PDF file or the like. Hereinafter, the term “job PS/PDF file” refers to the job file.
In the print field, a CMYK (i.e. Cyan, Magenta, Yellow and Black printing ink) color model is used for color separation overprint. The definition of the overprint directly influences the quality of final products. To this end, collimating marks are generally added around pages to be printed. Besides, other marks like clipping marks, step wedges may be added, too.
Generally, there are three methods for adding marks. One is to directly arrange marks required by the back-end output in the front-end plate making software so that the job PS/PDF filed with a RIP includes the arranged marks. Those arranged marks actually become a part of page content in the RIP. Another is to preprocess a job file before the job PS/PDF file is filed with a RIP so that a PS stream describing marks is inserted into a page PS stream. In this way, the PS stream describing marks actually becomes a part of the preprocessed job file. The common feature of the two methods is that a job PS/PDF file filed with a RIP contains marks already, namely, the marks are added to a page before the page is rasterized by a RIP and the RIP is not responsible for adding marks. The third method is to splice stored mark bitmaps onto page bitmaps to generate the final bitmaps.
All the methods above have limitations. In the first one, an operator should be good at making plates and familiar with back-end output devices and post-press processes. On the other side, operators don't know, from time to time, what kind of back-end output devices and post-press processes will be used when plates they made are completed. This is so-called “separating editing from printing” work model, namely, making plates and editing are separated. This model does not allow operators adding marks during making plates. Instead, marks have to be added by those operators who operate back-end output devices.
Pre-processing of the second method is hard to adapt to the PS files generated by various existing typesetting software, especially to those multi-page PS files whose page description of each page is not independent. Adding marks by said pre-processing needs to add the PS stream describing the marks at the end of the page description PS stream of every page. However, the two PS streams are not compatible, resulting in that the pre-processed job file cannot be correctly interpreted in the RIP. Moreover, page-end symbols of PS files generated by different typesetting software are not uniform. Therefore, it is hard for the pre-processing program to find page-end symbols in the PS stream of the job file. It needs to specially process the PS files generated by various software or various versions of the same software. Therefore, this method cannot solve the problem of adding marks to any PS file. One more disadvantage of this method is that a job file should be pre-scanned, resulting in low efficiency.
The mentioned third method overcomes the problem of compatibility existing in the second method but the efficiency of the third becomes lower than the second one because the third one is to splice the mark bitmaps onto the page bitmaps to generate the final bitmaps. The size of the bitmaps to be processed becomes very large, especially in a raster device with high resolution.